This investigation extends a quantitative experimental model designed to analyze biological and physical aspects of repair in canine segmental fibular cortical bone grafts. Insignificant differences have been determined between bilateral autografts in contrast to bilateral grafts in which one is a fresh allograft, and secondly, that the immune response to fresh allogeneic grafts were abrogated with the continuous use of Imuran while normal autogenous graft repair was maintained. Using those results, studies will be conducted to determine if fresh allogeneic cortical grafts under relatively short-term immunosuppressed states with Imuran will mimic fresh cortical autografts physically and biologically in long-term in vivo states. The reparative features will be quantitated by continuous tetracycline labeling, microradiography, radiography, and torsional loading to failure. Finally, data on human bone grafts will continue to be collected on an available and appropriate basis with the attempt made to correlate the results to that found on an experimental basis.